This application is based upon and claims the benefit of priority from the prior Japanese Patent Application No. 2000-299425, filed Sep. 29, 2000, the entire contents of which are incorporated herein by reference.
1. Field of the Invention
The present invention relates to a vertical cavity-type semiconductor light-emitting device which emits a light vertical to a main surface of a substrate and an optical module using a vertical cavity-type semiconductor light-emitting device and resin molding.
2. Description of the Related Art
A resonant-cavity light-emitting diode (Hereinafter, described as an RCLED (Resonant-Cavity Light-Emitting Diode)) has a similar structure to a vertical-cavity surface-emitting laser (Hereinafter, described as a VCSEL (Vertical-Cavity Surface-Emitting Laser)). The RCLED can operate in an LED mode by setting reflectivity on the light emission-side low and suppressing laser oscillation. The RCLED has the following features by the effect of the resonator structure compared with the usual LED.
1) A line width of an emission spectrum is narrow.
2) A directivity of the output light is high.
3) A carrier lifetime of a spontaneous emission is short. Therefore, the RCLED is very suitable as the transmission light source for an optic LAN and an optical data link compared with the usual LED, and performs an important role at the transmission ratio of especially about 100 Mbps to 1 Gbps.
FIG. 1 shows a structural sectional view of a conventional RCLED emitting at wavelength regions around 660 nm. The RCLED shown in FIG. 1 has substantially the same configuration as that shown in IEEE PHOTONICS TECHNOLOGY LETTERS, VOL. 10, NO. 12, PP. 1685-1687. The RCLED shown in FIG. 1 has a structure in which an N-type GaAs buffer layer 108, an AlGaAs-based n-type distributed Bragg reflector type mirror 107 (Hereinafter, the distributed Bragg reflector type mirror is described as a xe2x80x9cDBR (Distributed Bragg Reflector) mirrorxe2x80x9d), an N-type InGaAlP clad layer 106, an InGaAlP-based MQW (Multi Quantum Well) active layer 105, an p-type InGaAlP clad layer 104, an AlGaAs-based p-type DBR mirror 103, and a p-type GaAs contact layer 102 are accumulated one by one on an n-type GaAs substrate 109. The current injection into the active layer is performed by a the p-side electrode 101 which has an opening for the light emission and an n-side electrode 110 provided on the entire back surface of the substrate. The current confinement to the emission region is performed by the high resistance semiconductor area 111 formed by using proton implantation. The current confinement size is about a diameter of 50 to 100 xcexcm. The DBR mirror comprises a structure in which an Al0.98Ga0.02As low refractive index layers and an Al0.5Ga0.5As high refractive index layers are alternately accumulated. The number of repetitions of accumulation is 30.5 (reflectivity about 99%) on the n-side and 10 (reflectivity about 90%) on the p-side.
In the vertical cavity-type light-emitting device whose emission wavelength is in a red wavelength region as mentioned above, to make the DBR mirror transparent for the emission wavelength, it is necessary to use AlGaAs whose Al composition is higher than 0.5 for both the low refractive index layer and the high refractive index layer. Furthermore, it is preferable to enlarge a difference of the refractive index between the low refractive index layer and the high refractive index layer as much as possible in order to widen the width of the high reflection band region of the DBR mirror sufficiently. Therefore, it is general that the Al composition assumes to be 1 or a value close to 1 in the low refractive index layer.
On the other hand, when making an optical transmission module using the light-emitting device like the RCLED, the resin molding or the hermetic sealing to the can package is used to protect the semiconductor light-emitting device. It becomes possible to be a small module with low-price by using the resin molding. However, the resin which is generally used has the problem in the humidity resistance. Therefore, it is difficult to manufacture the module with high reliability using the resin molding. Especially, in the vertical cavity-type semiconductor light-emitting device using AlGaAs in which the Al composition is high as mentioned above in the vicinity of the element surface, it is very difficult to manufacture the module with high reliability by the resin molding, since the degradation of the AlGaAs layer by moisture absorption is remarkable.
As described above, in a conventional vertical cavity-type semiconductor light-emitting device, since AlGaAs whose Al composition is high is used near the surface of the element, the degradation of the device by moisture absorption is very remarkable. Therefore, it is necessary to use not the resin molding but the hermetic sealing to create the module with high reliability. Therefore, the low price and the miniaturization of the module are difficult. Especially, when AlGaAs whose Al composition exceeds 0.5 is used, the degradation of the light-emitting device by the moisture absorption is very remarkable.
An object of the present invention is to provide a light-emitting device with high reliability.
The vertical cavity-type semiconductor light-emitting device according to an embodiment of the present invention is characterized by comprising: a first semiconductor distributed Bragg reflector type mirror formed on a substrate; a first semiconductor layer formed on the first semiconductor distributed Bragg reflector type mirror and including an active layer which at least becomes an emission layer; a second semiconductor distributed Bragg reflector type mirror formed on the first semiconductor layer and including Al as a configuration element; and a second semiconductor layer including InxGa1xe2x88x92xP (0xe2x89xa6Xxe2x89xa61) layer provided on the second semiconductor distributed Bragg reflector type mirror.